1. Field of the Invention
The present invention relates to a method for estimating repair accuracy of a mask shop, which provides a basis for engineers to determine a qualified mask shop.
2. Description of the Prior Art
Masks are frequently used in a semiconductor manufacturing process. A typical mask comprises a transparent substrate such as a quartz substrate and a light-shielding or absorbing layer such as a chrome layer with a thickness of 1000 Å on the substrate. A phase-shift mask further comprises a layer generating a phase shift for the light penetrating therethrough.
A typical mask manufacturing process comprises the steps of depositing a chrome layer on a quartz substrate, depositing a photoresist layer on the chrome layer, patterning the chrome layer by etching under the masking of the photoresist layer processed by e-beam writing and developing.
Defects on the chrome layer are usually generated after the previously described steps. They include clear defects which are missing parts of the chrome layer and opaque defects which are redundant parts of the chrome layer. A further step of chrome depositing is needed to repair the clear defects. As for repair of the opaque defects, a step of chrome sputtering using FIB (Focus Ion Beam) is implemented.
As shown in FIG. 1, the step of chrome depositing is implemented for repairing a clear defect on a line 121 of a chrome layer 12 on a quartz substrate 11. A gentle slope of chrome, rather than a sharp wall, is formed where the clear defect is repaired and some chrome particles are scattered on the quartz substrate 11 in the vicinity of the area where the defect is repaired. Thus, a contaminated area 111 which deteriorates the transparency of the quartz substrate 11 is formed.
The repair accuracy of the mask shop is very important due to the shrinkage of ICs and since defects of the chrome layer always exist. Engineers are eagerly to have a estimation basis of the repair accuracy to determine a qualified mask shop.